The current phase of this project involves continuing studies on the effects of selective brain lesions on production of the Isolation Peep. Since lesions in the thalamus and midbrain that disrupt production of this vocalization also may encompass fibers arising from more rostral structures, it is important to determine the effects on the Isolation Peep of damage to these rostral structures, particularly the anterior limbic cortex. We have attempted to deactivate the anterior limbic cortex in one subject by surgically occluding the anterior cerebral artery. Postoperatively, this animal failed to utter Isolation Peeps until the third postoperative week, although other vocalizations were recorded during the intervening period. A new study assessed the role of opiates and opiate antagonists on Isolation Peep production. Preliminary results suggest that an opiate-dependent mechanism underlies production of the Isolation Peep. Another new study involved electrical stimulation of the cingulate gyrus in squirrel monkeys, attempting to locate brain structures that reliably produce vocalizations.